I discovered that adsorbed water molecules and microscopically small water droplets can be detected by measuring the galvanic current generated when a conductive material comes into contact with an array of dissimilar-metal wires separated by submicron gaps. Based on this principle, we demonstrated the early detection of condensation at its initial stages and the measurement of minute amounts of water vapor released from humans and plants. We are also investigating the detection of molecules other than water, as well as their aggregation structures, phase transitions, and electrical conduction mechanisms.